Sima de los Huesos hominins: ~430 thousand years old and on the Neandertal lineage

Seventeen Middle Pleistocene crania from the Sima de los Huesos site (Atapuerca, Spain) are analyzed, including seven new specimens. This sample makes it possible to thoroughly characterize a Middle Pleistocene hominin paleodeme and to address hypotheses about the origin and evolution of the Neandertals. Using a variety of techniques, the hominin-bearing layer could be reassigned to a period around 430,000 years ago. The sample shows a consistent morphological pattern with derived Neandertal features present in the face and anterior vault, many of which are related to the masticatory apparatus. This suggests that facial modification was the first step in the evolution of the Neandertal lineage, pointing to a mosaic pattern of evolution, with different anatomical and functional modules evolving at different rates.

8 comments:

Something I don't understand (and I can't access the article). They seem to be suggesting that it's on the Neandertal side of the Denisovan-Neandertal split, but how could we possibly know than when we know next to nothing about Denisovan morphology? Maybe Denisovans also had the synapomorphies shared by Neandertals and the Sima de los Huesos hominins. These could have split off before the Neandertal-Denisovan split. Or, as the mtDNA suggests, they could even be on the Denisovan side.

The conclusions of this study would be hilarious if we were not talking about serious science. For something like half a century, the general mainland European view has been: the overwhelming evidence is that there is a species or group, heidelbergensis, that is clearly (and still, to date, using modern methods) identifiable among other fossils, that lived in Europe and Asia (and with similar specimen in Africa) from about 800,000 to <200,000 ya. Here, 800,000 to 600,000 ya is a transition period during which it developed a larger brain case volume and distinct cultural traits rather different from erectus, and ~4000,000 - 200,000 ya is a transition period during which a distinct subgroup, Neanderthals, developed -- first in the extreme west of the heidelbergensis domain during an extended cold spell. These then propagated eastward towards West Asia and all the way to Siberia, in part extinguishing local heidelbergensis signatures, and in part preventing AMHs entry into that region. Note that true Neanderthals are witnesses of the continuing genetic exchange between European, W Asian, and African heidelbergensis until about 400 - 350 kya (during accommodating climate), since they carry mtDNA more similar to AMHs than to the original European heidelbergensis (-> Denisovans, which, incidentally, the S-H population shares). For years the Sima de los Huesos researchers have been trying hard to convince others that they have something special: a different people, a different taxon, a different origin of early European hominins. But in the end, their research always converges with the age-old mainstream European consensus view. If they only would open their eyes.

We seem to have here a classic example of Darwinian gradual evolution rather than punctuated equilibrium. The change was driven by gene flow from a variety of populations as shown in the Science Daily article:

http://www.sciencedaily.com/releases/2014/06/140619142204.htm

"This 'mosaic pattern' supports a theory of Neandertal evolution that suggests Neandertals developed their defining features separately, and at different times -- not all at once".

And:

"'One thing that surprised me about the skulls we analyzed,' Arsuaga said, 'is how similar the different individuals were. The other fossils of the same geological period are different and don´t fit in the Sima pattern. This means that there was a lot of diversity among different populations in the Middle Pleistocene. ... Indeed, other European Middle Pleistocene Homo sapiens do not exhibit the suite of Neandertal-derived features seen in this fossil group. Thus, more than one evolutionary lineage appears to have coexisted during the European Middle Pleistocene, with that represented by the Sima sample being closer to the Neandertals'".

As others have noted elsewhere in the blogosphere, reconciling this with the ancient mtDNA data requires a more complex story than one would have suspected because the Neanderthal-modern human clade breaks from the Denisovan-Heidelbergus clade in the ancient mtDNA lineages.

"reconciling this with the ancient mtDNA data requires a more complex story than one would have suspected"

I have long assumed our evolution has been no simple process. This link shows even the change from 'ancient' to 'modern' human was far from simple:

http://www.unz.com/gnxp/whole-genomes-as-a-window-into-the-past/

Quote:

"This suggests that there was a lot of population structure and gene flow within Africa before the expansion of Eurasians. Not surprising, but it is another nail in the coffin of the idea that modern humans emerged in a punctuated fashion and exploded from a singular tribe in eastern or southern Africa".

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